1. Field of the Invention
The present invention relates to a cylinder screen printing machine, and more particularly to a paper discharger in such a printing machine, capable of easily cleaning the underside of a screen plate and easily removing any dirt from the peripheral surface of a cylinder.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings schematically shows a conventional cylinder screen printing machine. One of stacked sheets of printing paper 101 is fed by a paper feed belt 2 from an automatic paper feeder 1 to a cylinder 3. The sheet of printing paper 101 is positioned immediately in front of the cylinder 3 as shown in FIG. 2. The paper feeding and positioning device are omitted from illustration as it has no bearing on the present invention.
The cylinder 3 is rotated about its own axis in the direction of the arrow 102 or in the opposite direction by a sector gear 7 angularly movable back and forth by a crank 5 through a connecting rod 6 and a gear 8 attached to one end of the cylinder 3 and held in mesh with the sector gear 7. A screen plate 9 disposed upwardly of the cylinder 3 is reciprocably moved to and fro in the directions of the arrows 103, 104 by a reciprocating mechanism (not shown) in synchronism with the back-and-forth angularly movement of the cylinder 3.
In synchronism with the movement of the screen plate 9 in the direction of the arrow 103, the cylinder 3 is angularly moved about its own axis in the direction opposite to the arrow 102 to the position shown in FIG. 2. After a leading edge of the sheet of printing paper 101 is gripped by a paper gripper 4 attached to the cylinder 3, the cylinder 3 is rotated back in the direction of the arrow 102. At this time, a squeegee 10 is lowered toward the screen plate 9 at a position where the paper gripper 4 passes, to press the screen plate 9 as it moves in the direction of the arrow 104 for thereby squeezing ink down through the screen plate 9. The pattern on the screen plate 9 is thus printed on the sheet of printing paper 101 fed below the screen plate 9.
When the paper gripper 4 is opened in front of a paper guide 11 as shown by the phantom line in FIG. 2 after the cylinder 3 has rotated in the direction of the arrow 102, the sheet of printing paper 101 is allowed to move over the paper guide 11 as shown in FIG. 3 onto a paper discharge table 12 positioned downstream of the cylinder 3. The cylinder 3 is then rotated back after it has been rotated in the direction of the arrow 102 to the position illustrated in FIG. 3, and simultaneously the screen plate 9 is moved back in the direction of the arrow 103 after it has been moved in the direction of the arrow 104 to the position of FIG. 3. As the screen plate 9 is moved back in the direction of the arrow 103, the squeegee 10 is lifted and a doctor blade 103 is lowered to spread a uniform coat of ink over the screen plate 9.
Thereafter, the cylinder 3 is rotated again in the direction opposite to the arrow 102 to repeat the foregoing cycle of operation for printing.
With the prior arrangement as described above, the underside of the screen plate 9 is cleaned and any dirt on the peripheral surface of the cylinder 3 is removed either directly by hand inserted from a rear position into a space below the screen plate 9 or by an instrument in a process which takes a long period of time. When the screen plate 9 is positioned as shown in FIGS. 2 and 3, a space 105 between the screen plate 9 and the paper feed belt 2 and a space 106 between the screen plate 9 and the paper discharge table 12 are relatively small, rendering the cleaning procedure awkward and preventing the screen plate 9 and the cylinder 3 from being cleaned sufficiently. It has eventually been necessary to remove the screen plate 9 for cleaning the same and the cylinder 3.
When the screen plate 9 is to be attached again, its positioning and color registration at the time of printing have to be readjusted, a procedure which shortens the time required for printing and reduces the printing efficiency.
One way for an easy cleaning process is to enlarge the spaces 105, 106 below the screen plate 9. To this end, the paper feed belt 2 or the paper discharge table 12 may be lowered away from the screen plate 9. However, since the retraction of the paper feed belt 2 would cause interference with other components, it would be preferable to retract the paper discharge table 12 downwardly.
As shown in FIGS. 1 through 3, lateral frames are interconnected by a shaft stay 17 attached to rear ends thereof. The shaft stay 17 is positioned downwardly of the screen plate 9 and becomes an obstacle to the operation for cleaning the screen plate 9 and the cylinder 3. It is therefore desirable to remove the shaft stay 17 for facilitating the cleaning operation.